For over a decade, the HgCdTe research community has spent considerable effort to prepare CdTe/Si composite substrates for HgCdTe material growth and subsequent infrared (IR) device applications. These research efforts have led to a relatively mature process for CdTe/Si fabrication by MBE. CdTe/Si composite substrates have been used to fabricate large-format short wavelength infrared (SWIR, 1-3 μm) and medium wavelength infrared (MWIR, 3-5 μm) HgCdTe focal plane arrays, despite the lattice mismatch between CdTe and HgCdTe.
However, to advance this technology to long wavelength (LWIR, 8-12 μm) HgCdTe devices, lattice matching to HgCdTe is needed in order to reduce the dislocation density within the material. This is specifically necessary for LWIR material since an elevated dislocation density has a greater impact on device performance in the LWIR limit than in either MWIR or SWIR regions due to the inherently smaller band gap of long wavelength detecting HgCdTe material. To mitigate the lattice mismatch issue, initial efforts have focused on incorporating 4.3% Zn into the CdTe/Si layer to provide Cd0.957Zn0.043Te/Se composite substrates which are exactly lattice matched to LWIR HgCdTe. However, it is difficult to growth CdZnTe layers of suitable crystal quality and low defect levels on Si. Furthermore, the crystalline structure of Cd1-zZnzTe degrades for increasing values of z, perhaps due to a miscibility gap.
The II-VI compounds, using nomenclature common in the literature, include group II atoms (such as cadmium (Cd), zinc (Zn), and mercury (Hg)) in compounds formed with group VI atoms (such as sulfur (S), selenium (Se), and tellurium (Te)). These compounds are often semiconducting. Binary compounds include CdTe, CdSe, CdS, ZnTe, and the like. CdTe, for example, is sometimes referred to as cadmium telluride, with analogous nomenclature for other compounds. This nomenclature is not intended to indicate any particular electronic state of the group II or group VI (chalcogenide) atoms within the compound, or to suggest any other compound property. CdTe is sometimes also referred to as an alloy of cadmium and tellurium. The term alloy, in this context, does not suggest any particular property of the compound, and is only used to indicate that the compound includes the given atomic species.
Ternary II-VI compounds include compounds having two group II atomic species and one group VI atomic species, such as HgCdTe (mercury cadmium telluride, or MCT), and compounds having one group II atomic species and two group VI atomic species, such as CdSeTe. Generally, a term such as HgCdTe is used to represent a class of compounds having the general formula Hg1-yCdyTe, where 0<y<1, sometimes written (Hg,Cd)Te. Quaternary II-VI compounds include CdZnSeTe, HgCdSeTe, and other such compounds.
U.S. Pat. Nos. 5,306,386 and 5,399,206, both to de Lyon, disclose growth of a ternary or quaternary II-VI semiconductor layer on a silicon (Si) substrate having an arsenic monolayer coating. U.S. Pat. No. 6,045,614, also to be Lyon, discloses epitaxial growth of CdZnTe(1 1 1) on a silicon substrate having a (1 1 1) orientation tilted 2-8 degrees away from the surface normal.
However, the prior art fails to disclose the MBE growth of high quality CdSeTe and CdZnSeTe films on a silicon based substrate, having low surface defect density and potential lattice matching to HgCdTe. In this context, a silicon based substrate is a substrate including a silicon layer, such as a silicon wafer, a passivated Si layer, or a Si layer supporting one or more further layers, such as ZnTe, CdTe and/or CdSeTe and or CdZnSeTe. There exists a need for high-quality CdSeTe or CdZnSeTe composite materials that are lattice matched to Hg1-yCdyTe in the alloy composition a range 0≦y≦1.